Differential pressures must be measured in numerous technical applications. A generally known differential pressure-measuring device has a pressure sensor. The pressure sensor has two pressure- and separating membranes, which are spaced apart and each allocated to one delivery connection. A pressure-balancing medium is located in the space between the separating membranes. Situated on the side of the separating membranes facing away from the pressure-balancing medium is a respective space in which a first pressure prevails on the side of the first separating membrane, and a second pressure prevails on the side of the second separating membrane. In addition, the differential pressure-measuring device has integrated plate-type capacitors, whose capacity depends on the prevailing pressures. The capacity values for the plate-type capacitors are subjected to a capacitive evaluation to convert the corresponding pressures into a current signal, e.g., with values ranging from 4 to 20 mA, by finding the electrical difference.
This kind of structurally favorable embodiment makes it possible to measure the differential pressure of gases in piping that is connected to the differential pressure-measuring device, for example. The measurement of liquids with precipitating solids requires that a capillary line be arranged in each differential pressure-measuring device to avoid obstructions in the area of the delivery connections.
An embodiment of this type entails a correspondingly higher complexity of design and expense. When measuring a differential pressure between a container floor and container cover to determine a fill level with superposed pressure, the rising capillary also gives rise to a hydrostatic column, and hence a measuring error.
Another embodiment for a known differential pressure-measuring device consists of two conventional standard pressure-measuring devices with frontal, flush-mounted sensors each having a current output as an output for outputting measured data. The measured data are relayed to a separate electronic evaluator, wherein the electronic evaluator finds the difference between the currents. In this case, the difference between the current signal of the first pressure-measuring device and the current signal of the second pressure-measuring device is found with an analog circuit or a microprocessor. This kind of arrangement does not require a capillary line, thereby eliminating the otherwise resultant measuring error. However, the disadvantage here is that two stand-alone measuring devices and an additional evaluating device with electronic evaluator connected thereto are required, making installation complicated. The provision of a separate evaluating device results in additional costs.